Studies have shown that soccer players have a high prevalence of low back pain (LBP). However, physical characteristics (sagittal spinal alignment and hip joint range of motion [ROM]) associated with LBP have not been clarified. This study seeks to clarify the relationship between physical characteristics and LBP in high school male soccer players. The participants were 90 high school male soccer players. The presence of LBP was evaluated using a questionnaire. We assigned the participants into two groups: the non-LBP group (n = 58) and the LBP group (n = 32). Passive ROM of hip and sagittal spinal alignment were measured. Thoracic kyphotic angle (TKA) was significantly higher in the LBP group than in the non-LBP group, and the ROM of hip joint extension in the nondominant leg was significantly lower in the LBP group than in the non-LBP group. On logistic regression analyses, TKA in the upright position (adjusted odds ratio [OR]: 1.087, 95% confidence interval [CI]: 1.019–1.159, p < 0.01) and hip extension ROM deficits in the nondominant leg (adjusted OR: 0.888, 95% CI: 0.789–0.999, p < 0.05) were related to LBP in high school male soccer players as determined. This study suggests that hyperkyphosis in the upright position and hip extension ROM deficits in the nondominant leg were related to LBP in high school male soccer players.
The relationship between electromyographic (EMG) amplitude and exerted force has been established in numerous studies and used as fundamental knowledge to interpret the results of EMG in human movement. Recent neuroanatomical studies suggest that the individual hamstring muscles may be regionally regulated by the central nervous system. In fact, a few studies observed nonuniform EMG activities between regions along the length of the biceps femoris long head (BFlh) and semitendinosus (ST) during knee flexion exercise. However, it remains unknown whether the EMG-force relationship varies among regions of the individual hamstring muscles. This study aimed to compare the EMG-force relationship among regions of the individual hamstring muscles during knee flexion exercise. Thirteen healthy males performed isometric knee flexion at 20%–80% of maximal voluntary contraction (MVC). Surface EMG amplitudes in the proximal, middle, and distal regions of the biceps femoris long head, semitendinosus, and semimembranosus (SM) were assessed and normalized to the root mean square (RMS) during MVC as %RMS. The results showed that %RMS of BFlh was consistently higher in the distal regions than in the proximal region at 20%–80% of MVC (all: p < 0.05). In ST, %RMS in the middle and distal regions were higher than that in the proximal regions only at 20% of MVC (p < 0.05). Similarly, %RMS of SM was higher in the middle region than in the proximal region at 20% and 40% of MVC (all: p < 0.05). These results suggest that the EMG-force relationship is not consistent among regions of the individual hamstring muscles, especially between the proximal and distal regions of BFlh.
The aim of the present study was to clarify the factors affecting an increase in core body temperature during 40°C water immersion to the subclavian level. Fifteen healthy males were immersed in water for 60 min. Rectal temperature (Trec) and skin temperature (Tsk) at four skin sites were determined. Minute ventilation (VE) was measured, and metabolic rate was determined by indirect calorimetry. Skin blood flow and sweat rate at the forehead were assessed using laser-Doppler flowmetry (%LDFhead) and dew hygrometry (SRhead), respectively. Hot feeling was assessed with a visual analog scale. When Trec reached 39°C or participants reported an extremely hot feeling, the experiment was ceased. Eleven participants were unable to complete the protocol (ten participants due to Trec > 39°C; and one due to excessive hot feeling). Trec increased with immersion period. Mean Tsk was unchanged from 20 min. VE and metabolic rate increased with immersion period. %LDFhead and SRhead increased after immersion and remained unchanged from 15 and 30 min, respectively. Change in Trec from the baseline at 15, 30, and 45 min was correlated to cumulative change in metabolic rate from the baseline at 0-15, 0-30, and 0-45 min. No correlations were observed between change in Trec and cumulative changes in VE, %LDFhead, and SRhead from baseline, hot feeling, body weight and body composition. Water immersion at 40°C induced a large difference in the increase of Trec, in which metabolic responses to heat stress may be involved. The relationship between heat tolerance and change in Trec is different among individuals.
The purpose of this study was to clarify the effect of aerobic exercise training on the coldness of the body and physiologically-related factors in Japanese young women with cold constitution. Eighteen subjects were divided into two groups: exercise (E) and non-exercise control (C) groups. Subjects in the E group performed exercise training of fast walking 4 days or more per week for 4 weeks. The training significantly decreased the scores for cold feeling in the fingertips and toes, but did not change the metabolic rate or sublingual and skin temperatures in the hands and feet during rest under normothermic conditions. In the C group, all variables remained unchanged throughout the 4-week control period. These results suggest that aerobic exercise mitigated coldness in the distal portion of the extremities via the reduction of cold sensation at a normal body temperature in young women complaining of chilliness.
Urinary titin fragment concentration has been established as a noninvasive biomarker of muscle protein degradation and muscle damage after exercise. We hypothesized that concerning the microdamage in the chronic phase of muscle strain injury, muscle damage is more likely to occur after exposure to training workload. We aimed to evaluate the urinary titin fragment concentration in professional soccer players who previously had muscle strain injuries (injured vs uninjured group: mean ± SEM age [years], 26.25 ± 1.4 vs 23.75 ± 1.01; playing years, 14.375 ± 1.17 vs 12.25 ± 0.24; height [cm], 173.63 ± 1.98 vs 176.38 ± 1.0; weight [kg], 69.63 ± 2.05 vs 72.38 ± 1.87; mean body mass index [kg/m2], 23.0 ± 0.32 vs 23.25 ± 1.39). The urine titin N-terminal fragments of eight professional soccer players with a previous muscle strain and eight uninjured players were measured using enzyme-linked immunosorbent assay before and 12 h after general team training. The urinary titin fragment values before and after training and the change in the titin fragment-to-creatinine fragment ratio were compared between the groups. The initial urinary titin fragment value did not significantly differ between the injured (from 18,457.96 ± 3,615.54 to 115,480.29 ± 26,462.36) and uninjured groups (from 23,119.47 ± 8,107.72 to 46,206.32 ± 9,833.77); however, the urine titin fragment value and change in the changes in urinary titin fragment ratio from before to after training were higher in the injured group (Wilcoxon rank-sum test, p < 0.05). These findings may help guide the future management of athletes with previous muscle strain injuries. Urine titin fragment values could be used to evaluate athletes with previous muscle injury.
In the present study, we examined the biological maturity of young Japanese football players. In Japan’s football training system, players are selected at a young age. However, relatively early maturing players might be selected if the selection is based solely on technical and physical fitness factors. To eliminate this drawback in player selection, we believe that it is necessary to determine the players’ biological maturity accurately. Accordingly, the present study aimed to investigate the biological maturity of football players during the selection process. We included 475 young Japanese football players (mean age: 12.4 ± 0.6 years) affiliated with the Japan Professional Football League between 2007 and 2015. According to an unpaired t-test, there was no significant difference between the Tanner-Whitehouse 2 (Japan) skeletal age and the chronological age of the affiliated players. The difference in biological maturity between the junior youth (Jy) group (mean age: 12.9 ± 0.4 years [12.0–13.9]) and the junior (Jr) group (mean age: 11.8 ± 0.3 years [11.0–12.4]) was examined using a chi-squared test. The results of the residual analysis revealed a significant difference between the Jy and Jr groups (χ2 = 22.552, degree of freedom = 3, p < 0.01). We evaluated the biological maturity of young football players and examined the relationship between the differences in maturity and the timing of player selection. In the player selection process in this study, it was speculated that early maturing players may not always be easy to identify.
Standing desks have the potential to improve educational and health outcomes in elementary schools, yet limited intervention studies have been undertaken using mixed methods approaches or in Asian countries. The aim of this research was to elucidate the subjective experiences and objective effects of standing desk use in a Japanese elementary school. Respondents in the intervention included a class of 22 year six students and their teacher at a public elementary school in Nagano, Japan. Standing desks were implemented in the classroom for nine months. Subjective focus group and interview data were generated on two occasions during the intervention period to facilitate data saturation. Objective accelerometry data were used to record active and sedentary behaviour before and during the intervention. Focus group and interview data highlighted positive physical and educational effects, including perceived improvements in endurance and posture, self-expression, peer interaction, and reduced state anxiety. These data also revealed concerns about age-appropriateness and practicality of implementation in a conservative education system. Accelerometry findings showed significant changes in moderate- to vigorous-intensity physical activity during both school and non-school hours. Standing desks provide a practical approach for modernizing Japanese elementary education, which may hold benefits across both health and education. Follow-up multi-site randomized controlled interventions and comparisons of teacher style and philosophy in standing desk classrooms are recommended to confirm and expand the present findings.
Identifying the factors that contribute to individual differences in mid-level intensity neuromuscular fatigue is essential to improve performance and effective exercise in training and rehabilitation. This study investigated factors affecting individual differences in knee extensor fatigue induced by sustained isometric mid-level contractions. Twenty-six healthy young men performed a sustained fatiguing contraction to task failure at 40% maximal voluntary contraction (MVC) torque of the knee extensors. The MVC torque (TQMVC), evoked triplet torque (TQTRI), and voluntary activation (VA%) of the knee extensors were determined before and after the fatiguing task. Differences in TQMVC, TQTRI, and VA% before and after the fatiguing task were examined, and the relationship between TQMVC and TQTRI or VA% after the fatiguing task normalized to baseline was examined using Pearson product-moment correlation analysis. TQMVC and TQTRI decreased significantly after the fatiguing task (31.1% decrease for TQMVC, 38.8% decrease for TQTRI, p < 0.001), whereas VA% did not change significantly (4.2% increase for VA%, p = 0.057). After the fatiguing task, the normalized TQMVC was significantly correlated with the normalized TQTRI (r = 0.617, p < 0.001), but not with the normalized VA% (r = 0.348, p = 0.082). Individual differences in knee extensor fatigue induced by sustained mid-level contraction were more affected by peripheral fatigue than by central fatigue. Therefore, focusing on fatigue resistance in peripheral areas is important to improve endurance in moderate-intensity exercises.